1. Field of the Invention
The invention relates to a supporting structure for a roof rack for a vehicle, comprising two rails each of which consists of a rod member supported for being transversely pivotable at supports arranged at the ends thereof and being connected with a roof holding device.
2. Description of Related Art
Roof racks are mounted by the user to passenger cars when required. Two rails extending in the direction of motion and arranged adjacent and spaced from each other are provided and form a railing to which transverse supports have to be connected at which the roof loads, e.g. bikes, suitcases or the like are attached. Generally, the assembling of the rails with transverse supports is effected with the aid of screwing elements and pipe clamping members. This is tedious and the reliability of the formed supporting structure depends on the mounting accuracy. In the course of time, screws may loosen and the stability and reliability of the supporting structure decrease. It often seems to be desirable to dismount the transverse supports because they cause wind noise and have unfavourable influence on aerodynamics. This causes additional inconveniences by dismounting work, and moreover, the transverse supports have to be stowed somewhere. If they are stowed in the garage, e.g., they are not present when necessary; the vehicle storing capacity, however, is reduced when they are carried in the vehicle.
In order to overcome this disadvantage, a roof supporting system has been developed (DE 38 14 799 C2), wherein each rail comprises a longitudinally extending trough-like chamber for receiving support rods being supported at the rail and arranged for being pivoted around a vertical axis and which can be swung out to form a transverse support. With its free end, each support rod is secured in the opposite rail; as a consequence, the stationary securing points of the transverse supports invariably determine the distances between two transverse supports so that adaptations to the dimensions of the roof or the roof load are impossible. If they are not used, they are swung back into the trough-like chambers. It is a disadvantage of this configuration that the rail comprising the trough-like chamber must have considerable cross-sectional dimensions so that support rods of sufficient stability can be received therein. The weight of a rail with encased support rods is high, so that such roof supporting systems are only suitable for high-class vehicles and inappropriate for small or middle-class vehicles.
In another known supporting structure (DE 36 41 745 C2), it is provided that the longitudinal rails of two parallel railings are pivotable about vertical axes, so that they can act as transverse supports. After being pivoted, the longitudinal rail is engaged and locked in catch points of the opposite railing with its free end. Again, the stationary securing points determine the mutual distance between two transverse supports and distance variations for adapting the roof rack to different dimensions of the roof or loads to be received are impossible. Further, this roof rack requires high supports for the longitudinal rails in order to offer sufficient free space in case of them being pivoted about the vertical axis to migrate over the transverse crowning of the roof. The height of the supports and the involved elevated arrangement of the roof rack is not only unfavourable in case of loading and unloading, but it may also result in noise formations and changes in the driving qualities of the vehicle.
It is an object of the invention to improve a supporting structure such that the transverse supports may have any mutual distance for being adaptable to different roofs and/or roof load dimensions.